BLADE-ON-PETIOLE interacts with CYCLOIDEA to fine-tune <i>CYCLOIDEA</i>-mediated flower symmetry in monkeyflowers (<i>Mimulus</i>).

Abstract

Morphological novelties, or key innovations, are instrumental to the diversification of the organisms. In plants, one such innovation is the evolution of zygomorphic flowers, which is thought to promote outcrossing and increase flower morphological diversity. We isolated three allelic mutants from two <i>Mimulus</i> species displaying altered floral symmetry and identified the causal gene as the ortholog of <i>Arabidopsis BLADE-ON-PETIOLE</i>. We found that MlBOP and MlCYC2A physically interact and this BOP-CYC interaction module is highly conserved across the angiosperms. Furthermore, MlBOP self-ubiquitinates and suppresses <i>MlCYC2A</i> self-activation. MlCYC2A, in turn, impedes MlBOP ubiquitination. Thus, this molecular tug-of-war between MlBOP and MlCYC2A fine-tunes the expression of <i>MlCYC2A</i>, contributing to the formation of bilateral symmetry in flowers, a key trait in angiosperm evolution.